The goal of this study is the development of materials and coatings which will release heparin and anti-platelet drugs at a nearly constant rate. The polymer chosen as the carrier is poly-(dl-lactic acid) (PLA) which degrades slowly in the body giving innocuous end products. Copolymers with glycolic aci can be used for faster polymer disappearance, which can be varied from a week to at least a year. The major clinical goal in the use of these materials in fabricating small-vessel prostheses (less than 4 mm ID), by using them as a coating or as drug releasing fibers in the structure. The drugs would prevent thrombus formation while the polymer base slowly degraded, gradually exposing the prosthesis surface to the blood. There is evidence that such exposure will result in the smoother, thinner neointima required for small-vessel protheses. Heparin has been incorporated as fine particles into PLA to achieve the desired release rates. A new family of active platelet inhibitors has been synthesized, having controllable solubilities. Hydrophobic ones form solid solutions with PLA, giving long-term release, and showing the possibility of inclusion in other polymers. Polyester inferior vena cava patch grafts coated with drug-releasing PLA were inserted in dogs. They showed no clot adhesion to the surface, but showed the usual suture line adhesion. Attempts will be made to use a fast-releasing (one week) formulation as a top layer to overcome the clotting promotors coming from the injured tissue while endothelial healing occurs. For fast feedback to prosthesis coating forumulation, it is proposed to work in the superior vena cava of dogs, then study promising materials in peripheral veins. Long-term tests will be carried out in the carotid and femoral arteries.